Sulfur-containing thin films

ABSTRACT

In some aspects, methods of forming a metal sulfide thin film are provided. According to some methods, a metal sulfide thin film is deposited on a substrate in a reaction space in a cyclical process where at least one cycle includes alternately and sequentially contacting the substrate with a first vapor-phase metal reactant and a second vapor-phase sulfur reactant. In some aspects, methods of forming a three-dimensional architecture on a substrate surface are provided. In some embodiments, the method includes forming a metal sulfide thin film on the substrate surface and forming a capping layer over the metal sulfide thin film. The substrate surface may comprise a high-mobility channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/651,203, filed Jul. 17, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/992,942, filed Jan. 11, 2016, now U.S. Pat. No.9,721,786, which is a continuation of U.S. patent application Ser. No.14/133,509, filed Dec. 18, 2013, now U.S. Pat. No. 9,245,742, each ofwhich is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates generally to the field of semiconductor devicemanufacturing and, more particularly, to metal sulfide films and methodsfor forming sulfur-containing thin films, such as by atomic layerdeposition (“ALD”) processes. For example, metal sulfide films such asMgS films may be formed by ALD processes and may serve as an interfacelayer between a substrate and a dielectric layer.

Description of the Related Art

In an effort to continue to enhance the performance of high-k metal gatetechnology, the semiconductor industry has shown interest inhigh-mobility substrate materials, such as germanium, which exhibitsdesirable hole mobility, and group III-V materials, which exhibitdesirable electron mobility. Suitable group III-V materials include, forexample, GaAs, InP, InGaAs, InAs, and GaSb. However, problems with thesenew channel materials can be present at the interface between thehigh-mobility material and the overlying dielectric layer.

The high-mobility semiconducting channel, based on materials such as Geand InGaAs, have a very high number of interface states. These statestend to pin the Fermi energy and can severely deteriorate the functionof electronic devices. Sulfur passivation can be an efficient approachto minimize the interface states. Beyond passivating the surface, aninterface layer is desirable for integration with a high-k dielectriclayer. However, known interface layers have a variety of problems, suchas not preventing oxidation of the underlying high-mobility channel andallowing for undesirable current leakage or charge trapping and notpreventing up diffusion of group III-V elements or Ge into the gatedielectric.

SUMMARY OF THE INVENTION

In some aspects, methods of forming a metal sulfide thin film areprovided. According to some methods, a metal sulfide thin film isdeposited on a substrate in a reaction space in a cyclical process whereat least one cycle includes alternately and sequentially contacting thesubstrate with a first vapor-phase metal reactant and a secondvapor-phase sulfur reactant. In some embodiments, the metal reactantcomprises a metal selected from the group consisting of Mg, Ca, Y, Sc,Sr, Ba, La, and other lanthanides.

In some embodiments, a method for forming a metal sulfide thin filmincludes removing excess vapor-phase metal reactant and reactionbyproducts from the reaction space after contacting the substrate withthe first vapor-phase metal reactant. In some embodiments, excessvapor-phase sulfur reactant and reaction byproducts from the reactionspace after contacting the substrate with the second vapor-phase sulfurreactant. In some embodiments, the second reactant is introduced intothe reaction space before introducing the vapor-phase metal reactantinto the reaction space in at least one deposition cycle.

According to some embodiments, the metal sulfide film is formed using ametal reactant having at least one cyclopentadienyl (Cp) ligand. In someembodiments, the metal of the metal sulfide thin film is magnesium (Mg).In some embodiments, the metal reactant is Mg(Cp)₂ or a derivativethereof. In some embodiments, the metal reactant comprises Cp or aderivative thereof and the metal is Ca, La or another lanthanide, Sc, orY. In some embodiments, the metal reactant includes a metal that is notpresent in the portion of the substrate surface upon which the metalsulfide thin film is being formed.

According to some embodiments, a method for forming a metal sulfide thinfilm includes H₂S as a sulfur precursor or reactant. In someembodiments, the second reactant, or sulfur precursor, comprises sulfuratoms, sulfur-containing plasma, or sulfur-radicals. In someembodiments, the resulting metal sulfide thin film comprises MgS.

According to some embodiments, the substrate surface on which the metalsulfide film is deposited does not include silicon. In some embodiments,the substrate surface comprises InGaAs. In some embodiments, the metalsulfide thin film comprises more than one metal. In some embodiments,the metal sulfide thin film comprises non-metals in addition to sulfur,such as oxygen or nitrogen. In some embodiments, a method for forming ametal sulfide thin film includes subjecting the substrate to apretreatment reactant either ex situ or in situ prior to depositing themetal sulfide thin film. In some embodiments the metal sulfide film issubjected to a post-treatment reactant after deposition.

In some embodiments, the metal sulfide thin film has a thickness ofbetween about 1 Å and about 20 Å.

In some aspects, methods of forming a magnesium sulfide thin film areprovided. In at least some methods, the magnesium sulfide thin film isformed on a substrate in a reaction space in one or more depositioncycles. In some embodiments, the deposition cycles include providing avapor-phase magnesium reactant to the reaction space, removing excessvapor-phase magnesium reactant and reaction by-products, providing asecond reactant comprising sulfur to the reaction space, and removingexcess second reactant and reaction by-products.

According to some embodiments, the second reactant is provided to thereaction space before providing the vapor-phase magnesium reactant tothe reaction space. In some embodiments, the magnesium sulfide thin filmcomprises at least one metal other than magnesium. In some embodimentsthe magnesium sulfide film comprises at least one non-metal elementother than sulfur, such as nitrogen or oxygen.

In some aspects, methods of forming a three-dimensional architecture ona substrate surface are provided. In some embodiments, the methodincludes forming a metal sulfide thin film on the substrate surface andforming a capping layer over the metal sulfide thin film. In someembodiments, the substrate surface comprises a high-mobility channel. Insome embodiments, the metal of the metal sulfide thin film comprises atleast one of the following: beryllium, magnesium, calcium, strontium,scandium, yttrium, and lanthanum.

According to some embodiments, a method of forming a three-dimensionalarchitecture includes subjecting the substrate surface to a pretreatmentprocess prior to forming a metal sulfide thin film on the substratesurface. In some embodiments, the pretreatment process comprisessubjecting the substrate surface to at least one of the followingpretreatment reactants: (NH₄)₂S, H₂S, HCl, HBr, Cl₂, and HF. In someembodiments, the pretreatment process comprises exposing the substratesurface to at least one pretreatment reactant for a period of betweenabout 1 second and about 600 seconds, preferably between about 1 secondand about 60 seconds. In some embodiments, after forming a capping layerover the metal sulfide thin film, a barrier layer is formed over thecapping layer. Some embodiments include, after forming a capping layerover the metal sulfide thin film, forming a metal gate over the cappinglayer. Some embodiments include subjecting the metal sulfide thin filmand the capping layer to a post deposition treatment comprising anannealing process or a gas forming process.

In some embodiments, the metal of the metal sulfide thin film isdifferent from the metal or metals of the underlying substrate surface.In some embodiments, the metal of the metal sulfide thin film isdifferent from the metal or metals of the subsequently formed cappinglayer. In some embodiments, the metal of the metal sulfide thin film isthe same as at least one of the metal or metals of the subsequentlyformed capping layer. According to some embodiments, the capping layercomprises a high-k dielectric material. And in some embodiments, thesubstrate surface comprises a high-mobility channel.

In some embodiments, the metal of the metal sulfide thin film comprisesat least one of the following metals: Be, Mg, Ca, Ba, Sr, Y, Sc, La, Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Zn, Cd, Pb,In, Ga, Ge, Gd, Ta, Mo, and W. According to some embodiments, the metalsulfide thin film has a thickness between about 5 Å and about 20 Å.

In some aspects, methods of forming a three-dimensional architecture ona substrate surface are provided. Some methods include forming a metalsulfide thin film on the substrate surface using an ALD process andforming a capping layer comprising a high-k dielectric material over themetal sulfide thin film. In some embodiments, the metal of the metalsulfide thin film comprises at least one of the following metals: Be,Mg, Ca, Ba, Sr, Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, Al, Si, Zn, Cd, Pb, In, Ga, Ge, Gd, Ta, Mo, and W. In someembodiments, the metal sulfide thin film is formed using a sulfurprecursor selected from the following: elemental sulfur, sulfur plasma,H₂S, and (NH₄)₂S.

According to some embodiments, the method includes subjecting thesubstrate surface to a pretreatment process prior to forming a metalsulfide thin film on the substrate surface, wherein the pretreatmentprocess comprises exposing the substrate surface to at least one of thefollowing: HCl, HF, H₂S, HBr, Cl₂, and HF. In some embodiments, themethod includes subjecting the previously formed capping layer and metalsulfide thin film to a post deposition treatment, wherein the postdeposition treatment comprises exposure to at least one of the followingcompounds or processes: HCl, HF, H₂S, (NH₄)₂S, H₂ plasma, NF₃, thermalH₂ bake, and an annealing process. Some methods include, after forming acapping layer over the metal sulfide thin film, forming a metal gateover the capping layer, wherein the metal gate comprises at least one ofthe following: Ti, Al, Zr, Hf, V, Ta, Nb, Cr, Mo, W, Co, TiN, TiC,TiAlC, TaC, TaAlC, NbAlC, TiAl, TaAl, TaN, TaCN, WN, and TiWN.

According to some embodiments, the metal of the metal sulfide thin filmis different from one or both of the metal or metals of the underlyingsubstrate surface and the metal or metals of the capping layer. In someembodiments, the substrate surface comprises a high-mobility channel,wherein the high-mobility channel includes germanium or a III-Vmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the detailed descriptionand from the appended drawings, which are meant to illustrate and not tolimit the invention, and wherein:

FIG. 1 is a schematic representation of a gate stack that includes aninterfacial layer.

FIG. 2 is a flow chart illustrating an ALD process for forming a metalsulfide thin film according to some embodiments.

FIG. 3 is a flow chart illustrating an ALD process for forming amagnesium sulfide thin film according to some embodiments.

FIG. 4 illustrates an exemplary process for forming a three-dimensionalarchitecture according to the present disclosure.

FIG. 5 illustrates a capacitance vs. voltage curve with a frequencydispersion range from 100 Hz to 1 MHz for an interfacial layer.

FIG. 6 illustrates a capacitance vs. voltage curve with a frequencydispersion range from 100 Hz to 1 MHz for a sulfur-containing thin filmaccording to one embodiment of the present disclosure.

DETAILED DESCRIPTION

In some embodiments, metal sulfide films and methods of forming metalsulfide thin films are provided. In some embodiments, the metal of themetal sulfide thin film may be selected from any number of metals, suchas beryllium, magnesium, yttrium, calcium, strontium, barium, lanthanumand other lanthanides (such as cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium), silicon, zinc,cadmium, lead, indium, gallium, germanium, tantalum, molybdenum, andtungsten.

In some embodiments, a metal sulfide film is used as an interface layer,for example between a substrate and a dielectric layer. In someembodiments, the interface layer comprises a part of a gate stack. Insome embodiments, the interface layer is located between a dielectriclayer and a high-mobility channel. FIG. 1 illustrates a common gatestack configuration 100 that is formed on a substrate 110. A highmobility channel 115 is located between a source 120 and a drain 130. Ametal sulfide interface layer 140 may be included between thehigh-mobility channel and the dielectric layer 150. A metal gate 160 ispresent over the dielectric layer 150. In some embodiments the metalsulfide interface layer 140 may be formed using the methods describedherein.

In some embodiments, the metal in the metal sulfide thin film is chosenso as to be distinct from the metal in the underlying portion of thesubstrate. For example the metal in a metal sulfide film may bedifferent from any metal in an underlying high-mobility channel. In someembodiments the metal in the metal sulfide film may be different fromthe metal in an overlying dielectric layer. In some embodiments a metalsulfide interlayer may comprise a metal that is different from any metalin an underlying channel region of the substrate and from an overlyingdielectric layer.

In some embodiments a metal sulfide interface layer comprises one ormore of MgS, CaS, ScS_(x), YS_(x), LaS, a lanthanide sulfide, Al₂S₃,SiS₂, ZnS, CdS, SrS, CaS, BaS, PbS, In₂S₃, Ga₂S₃, GeS₂, Gd₂S₃, TaS₂,MoS₂ and WS₂. In some embodiments when a metal sulfide thin film forms apart of a three-dimensional architecture, particular metals areexpressly avoided, such as cesium and/or aluminum.

In some embodiments, suitable interfacial layers comprise a metalsulfide material that may protect the underlying high-mobility substratematerial from undesirable oxidation. In some embodiments, the metalsulfide thin film may be considered a passivation layer. In someembodiments, gate stacks formed with the presently disclosed interfaciallayers exhibit reduced leakage or reduced charge.

The presently disclosed metal sulfide films may be incorporated into avariety of integrated circuit architectures, such as FINFETs, planartransistors, vertical nanowire transistors, capacitors, powertransistors, etc.

In some embodiments, the methods for forming metal sulfide thin filmscomprise an ALD process. For example, a substrate may be alternately andsequentially contacted with a first reactant comprising metal (alsoreferred to as a metal precursor) and a second reactant comprisingsulfur (also referred to as a sulfur precursor). The metal precursor maybe selected to provide the desired metal in the metal sulfide interfacelayer. Thus, in some embodiments the metal reactant is selected toprovide a metal that is different from a metal in the underlyingsubstrate region and/or from a metal in a dielectric layer that is to besubsequently deposited. In some embodiments a metal sulfide filmcomprising one or more of MgS, CaS, ScS_(x), YS_(x) and lanthanidesulfides is deposited by an ALD process.

In some embodiments, methods of forming a metal sulfide film comprise anALD cycle in which a metal source chemical and a sulfur source chemicalare alternatively and sequentially pulsed into a reaction spacecomprising a substrate. The metal source chemical is provided to thereaction space where at least some of the metal source chemical contactsand adsorbs to the substrate surface. The sulfur source chemical issubsequently provided to the reaction space and reacts with the adsorbedmetal source chemical to form metal sulfide. In some embodiments, thesulfur source chemical may precede the metal source chemical. In somesuch embodiments the sulfur may bond to the substrate and the subsequentmetal source chemical reacts with the deposited sulfur, or the sulfursource chemical may change or remove and replace the surface terminationto SH_(x)-groups or other surface species comprising sulfur.

In some embodiments, reactants and reaction by-products are removed fromthe reaction space between provision of the metal source chemical andthe sulfur source chemical. Removal may occur before and/or after eachreactant pulse. Reactants and reaction by-products may be removed withthe aid of a purge gas and/or by subjecting the reaction space to a lowpressure produced by a vacuum pump to evacuate the reaction space.

The step of exposing the substrate to a metal source chemical may bereferred to as a metal phase, and the step of exposing the substrate toa sulfur source chemical may be referred to as a sulfur phase. In someembodiments, it may be desirable to repeat one or both of the metalphase and the sulfur phase one, two, three, four, five or more timesbefore proceeding to the next phase.

Such an ALD cycle is repeated as desired to form a film of a desirablethickness. In some embodiments, the ALD cycle is repeated until acomplete, closed layer of a metal sulfide is formed. In someembodiments, the ALD cycle is repeated until a physically continuouslayer of a metal sulfide is formed. In some embodiments, the ALD cycleis repeated until a minimum thickness is reached in which the depositedlayer gives desired electrical properties. In some embodiments, thedesirable thickness will be a thickness considered thick enough tocompletely cover a channel area of the substrate surface. In someembodiments, the desirable thickness is a thickness sufficient tosubstantially prevent oxidation of the underlying channel material ofthe substrate, such as during subsequent processing.

In some embodiments, a substrate surface may be subjected to apretreatment process. In some embodiments, a pretreatment processcomprises exposing the substrate surface to a pretreatment reactant thatremoves undesirable contaminants and/or prepares the substrate surfacefor the subsequent formation of a metal sulfide layer. A pretreatmentmay comprise, for example, providing one or more of a pulse or a rinseof HCl, HF, or a sulfur-containing compound, such as H₂S. In someembodiments, a pretreatment may comprise a sulfur passivation process.

In some embodiments, metal sulfides are formed that consist essentiallyof metal and sulfur. In some embodiments, additional reactants may beused to incorporate into or contribute other materials to the film, forexample oxygen to form metal oxysulfides. In some embodiments a compoundmetal sulfide may be formed, comprising two or more different metals.For example, a metal sulfide film may comprise AlMgS, MgSiS or MgHfS. Insome embodiments where additional non-metal elements in addition tosulfur are desired, an ALD process for forming the metal sulfide thinfilm may comprise phases in addition to the initial metal and sulfurphases. For example, they may include an oxidation phase where metaloxysulfides are desired. In an oxidation phase, oxygen or anoxygen-containing precursor is provided in the reaction chamber andallowed to contact the substrate surface. The oxygen phase may be partof one or more deposition cycles. In some embodiments, a separatenitrogen phase may be included in one or more deposition cycles. In someembodiments a second metal phase may be provided in one or moredeposition cycles. The oxidation phase, or other desirable phase, mayfollow the metal phase or the sulfur phase, but in either situation, itis desirable in some embodiments, to remove excess oxygen (or otherreactant) and any reaction by-products from the reaction space beforeproceeding to the next phase. In some embodiments an additional phase,such as an oxygen, nitrogen or additional metal phase may be providedafter the final deposition cycle, or intermittently in the depositionprocess.

According to some embodiments, a desirable metal sulfide of the presentdisclosure will include one or more metals and at least one element(such as oxygen or nitrogen) in addition to sulfur. Thus, ternary andquaternary compositions would serve as suitable metal sulfides. Examplesinclude, but are not limited to, MgHfOS, MgSN, etc.

In some embodiments, the deposited metal sulfide comprises at leastabout 5 at-% of sulfur, preferably more than about 15 at-% of sulfur andmore preferably more than about 30 at-% of sulfur and most preferablymore than about 40 at-% of sulfur. Depending on the metal oxidationstate the metal sulfide may comprise sulfur from about 45 at-% to about75 at-%.

In some embodiments, a magnesium sulfide (MgS_(x)) is formed. In someembodiments, the metal sulfide thin film may comprise other metals, suchas calcium, strontium, barium, lanthanum and/or other lanthanides, asdescribed in more detail elsewhere.

In some embodiments, such as where the metal sulfide thin film isincorporated into a three-dimensional architecture, metals in additionto those listed above may be considered for use in forming the metalsulfide thin film. Metals, such as yttrium, silicon, zinc, cadmium,lead, indium, gallium, germanium, tantalum, molybdenum, and tungstencould be suitably utilized. In some embodiments, the chosen metal may beselected based on, for example, the substrate and/or the dielectriclayer used in the architecture. For example, in some embodiments it isdesirable that the metal sulfide thin film, when acting as an interfacelayer between a high-mobility channel and a dielectric layer, utilize ametal that is distinct from the metals used in one or both the channeland the dielectric layer. In an embodiment where a three-dimensionalarchitecture is formed, it may be desirable to subject the high-mobilitychannel or substrate to a pretreatment prior to forming a metal sulfideinterface layer. A dielectric layer is then formed over the metalsulfide, and a post deposition treatment may be applied before, after,or before and after the formation of the dielectric layer. A subsequentlayer, such a metal gate can then be formed over the dielectric layer.

Geometrically challenging applications are also possible due to thenature of the ALD-type processes. The substrate surface may comprise oneor more three-dimensional structures. In some embodiments one or morestructures may have an aspect ratio of 1:1 to 10:1 or greater.

The film formed according to some embodiments is between about 1 Å andabout 20 Å; however, the actual thickness chosen may depend on theintended application of the thin film. In some embodiments a metalsulfide film is about 15 Å or less, for example about 10 Å. On the otherhand, in some applications a thickness greater than 20 Å, 30 Å, or even40 Å is desirable.

Atomic Layer Deposition (“ALD”) of Metal Sulfide Thin Films

ALD type processes are based on controlled, self-limiting surfacereactions and can provide precise control of the film composition. Gasphase reactions are avoided by contacting the substrate alternately andsequentially with reactants. Vapor phase reactants are separated fromeach other in the reaction chamber, for example, by removing excessreactants and/or reactant byproducts from the reaction chamber betweenreactant pulses. Removing excess reactants and/or reactant byproductsmay be achieved, for example, by purging the reaction space after eachpulse of reactant gas using a vacuum and/or a purge gas. A purge gas mayalso be flowed continuously before, during, and after each pulse ofreactant gas. For example, in some embodiments the purge gas may alsoserve as a carrier gas for one or more of the reactants.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure. Insome embodiments, the substrate surface on which deposition is to takeplace comprises silicon. In some embodiments the substrate surface onwhich deposition is to take place comprises germanium. In someembodiments, the substrate surface comprises one or more III-Vmaterials. In some embodiments, the substrate surface on whichdeposition is to take place comprises a high-mobility material. In someembodiments, the substrate surface comprises InGaAs. Other suitablesubstrate surfaces include, GaAs, InP, InAs, and GaSb. In someembodiments the substrate may be a 300 mm or a 450 mm wafer. In someembodiments, the substrate surface comprises multiple materials, such asone or more III-V materials, silicon, silicon oxide, silicon nitride,Si_(x)Ge_(1-x) or Ge.

Deposition temperatures are maintained below the precursor thermaldecomposition temperature but at a high enough level to avoidcondensation of reactants and to provide the activation energy for thedesired surface reactions. Of course, the appropriate temperature windowfor any given ALD reaction will depend upon the surface termination andreactant species involved. The reaction temperature may be from aboutroom temperature to about 500° C. or from about 20° C. to about 500° C.In some embodiments, the reaction temperature is from about roomtemperature to about 400° C. In some embodiments, the reactiontemperature is from about 150° C. to about 400° C., from about 200° C.to about 350° C., or from about 250° C. to about 300° C.

The reaction pressure may be from about 0.1 Torr to about 760 Torr. Insome embodiments, the reaction pressure may be from about 0.5 Torr toabout atmospheric pressure.

In some embodiments, at least one ALD cycle is used to form a metalsulfide thin film. The film formed according to some embodiments isbetween about 1 Å and about 20 Å; however, the actual thickness chosenmay be selected based on the intended application of the thin film. Insome embodiments, it is desirable to ensure that all or most of a targetsubstrate surface is covered by the interfacial layer. In such cases, itmay be desirable to form a film that is at least about 5 Å, preferably10 Å thick or greater than 10 Å. In some embodiments, thicknesses of 2Å, 3 Å, 4 Å, or even 5 Å will sufficiently cover the target substratesurface, e.g., a channel region. In some embodiments, such as where thefilm is to be incorporated into a capacitor, it may be desirable tolimit the film's thickness to no more than about 20 Å with 15 Å or even10 Å being the most desirable in some cases. It has been found, in somecases, that capacitance is undesirably reduced if too thick of a film isused. For other applications, thicknesses greater than about 20 Å may bedesirable. For example, films having a thickness of 30 Å, 40 Å, orgreater than 40 Å may be desirable in some applications, such as powertransistors. Because of the various constraints and advantages of thefilm's thickness, in some embodiments it may be desirable to form filmshaving a thickness that is between about 5 Å and about 10 Å. In someembodiments it may be desirable to form films with certain number ofdeposition cycles, such from about 5 deposition cycles to about 20deposition cycles, preferably from about 7 cycles to about 15 cycles,instead of a target thickness.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactant is supplied in each phase tosaturate the susceptible structure surfaces. Surface saturation ensuresreactant occupation of all available reactive sites (subject, forexample, to physical size or “steric hindrance” restraints) and thusprovides excellent step coverage. In some arrangements, the degree ofself-limiting behavior can be adjusted by, e.g., allowing some overlapof reactant pulses to trade off deposition speed (by allowing someCVD-type reactions) against conformality. Ideal ALD conditions withreactants well separated in time and space provide self-limitingbehavior and thus maximum conformality. In some embodiments, less than acomplete monolayer is deposited in one or more cycles, for example dueto steric hindrance. In some embodiments, more than one monolayer may bedeposited by, for example, adjusting the conditions to achieve somedecomposition reaction, such as would occur in CVD or CVD-likeprocesses. Limited CVD reactions mixed with the self-limiting ALDreactions can raise the deposition rate.

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400 Series reactor, available from ASM America, Inc of Phoenix,Ariz. and ASM Europe B. V., Almere, Netherlands. In addition to theseALD reactors, many other kinds of reactors capable of ALD growth of thinfilms, including CVD reactors equipped with appropriate equipment andmeans for pulsing the precursors can be employed. In some embodiments aflow type ALD reactor is used.

In some embodiments the reactor is a batch reactor and has more thanabout 50 substrates, more than about 100 substrates or more than about125 substrates. In some embodiments the reactor is a mini-batch reactorand has from about 2 to about 20 substrates, from about 3 to about 15substrates or from about 4 to about 10 substrates.

The metal sulfide ALD processes described herein can optionally becarried out in a reactor or reaction space connected to a cluster tool.In a cluster tool, because each reaction space is dedicated to one typeof process, the temperature of the reaction space in each module can bekept constant, which improves the throughput compared to a reactor inwhich is the substrate is heated up to the process temperature beforeeach run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

Preferably, for forming metal sulfide films, each ALD cycle comprises atleast two distinct phases. The provision and removal of a reactant fromthe reaction space may be considered a phase. For a metal depositioncycle, in a first metal phase, a first reactant comprising a suitablemetal—such as magnesium, calcium, strontium, barium, scandium, yttrium,or a lanthanide—is provided and forms no more than about one monolayeron the substrate surface. This reactant is also referred to herein as“the metal precursor,” “metal reactant,” or “metal source chemical” andmay be, for example, the corresponding beta-diketonate precursors andcyclopentadienyl-based precursors of the metals listed above. In asecond sulfur phase, a second reactant comprising sulfur is provided andmay convert adsorbed metal reactant to a metal sulfide. This reactant isalso referred to herein as “the sulfur precursor,” “sulfur reactant,” or“sulfur source chemical” and may be, for example, ammonia sulfide((NH₄)₂S), aqueous solution of (NH₄)₂S, or hydrogen sulfide (H₂S). Oneor more of the reactants may be provided with the aid of a carrier gas,such as N₂, Ar or He. Additional phases may be added and phases may beremoved as desired to adjust the composition of the final film.

The terms “first” and “second” may be applied to any particularprecursor depending on the sequencing of any particular embodiment. Forexample, depending on the embodiment the first reactant can be either ametal precursor or a sulfur precursor.

FIG. 2 illustrates that, according to some embodiments, a metal sulfidethin film is formed by an ALD-type process comprising multiple pulsingcycles 200, at least one cycle comprising:

-   -   pulsing a vaporized first metal precursor at step 220 into the        reaction chamber to form at most a molecular monolayer of the        metal precursor on the substrate,    -   purging the reaction chamber at step 230 to remove excess metal        precursor and reaction by products, if any,    -   providing a pulse of a second sulfur precursor to contact the        substrate at step 240,    -   purging the reaction chamber at step 250 to remove excess second        sulfur precursor and any gaseous by-products formed in the        reaction between the metal precursor layer on the substrate and        the second reactant, and    -   repeating the pulsing and purging steps at step 260 until a        metal sulfide thin film of the desired thickness has been        formed.

Purging the reaction chamber may comprise the use of a purge gas and/orthe application of a vacuum to the reaction space. Where a purge gas isused, the purge gas may flow continuously or may be flowed through thereaction space only after the flow of a reactant gas has been stoppedand before the next reactant gas begins flowing through the reactionspace. It is also possible to continuously flow a purge or non-reactivegas through the reaction chamber so as to utilize the non-reactive gasas a carrier gas for the various reactive species. Thus, in someembodiments, a gas, such as nitrogen, continuously flows through thereaction space while the metal and sulfur precursors are pulsed asnecessary into the reaction chamber. Because the carrier gas iscontinuously flowing, removing excess reactant or reaction by-productsis achieved by merely stopping the flow of reactant gas into thereaction space.

According to some embodiments, a metal sulfide thin film is formed by anALD-type process comprising multiple pulsing cycles, each cyclecomprising:

-   -   pulsing a vaporized first metal precursor into the reaction        chamber to form at most a molecular monolayer of the metal        precursor on the substrate,    -   providing a pulse of a second sulfur precursor onto the        substrate,    -   repeating the pulsing steps until a magnesium sulfide thin film        of the desired thickness has been formed.

In some embodiments, the ratio of metal precursor pulses to sulfurprecursor pulses is adjusted. Thus, in some embodiments, a metalprecursor is pulsed into the reaction chamber more than once relative tothe pulse of the sulfur precursor in at least one cycle. And in someembodiments, the sulfur precursor is pulsed into the reaction chambermore than once relative to the pulse of the metal precursor in at leastone cycle. For example, if increasing the amount of metal in the film isdesired, at least one ALD cycle, every other ALD cycle, or every third,fourth, fifth, sixth cycle, etc. could include one or more additionalmetal precursor pulses. Similarly, if increasing the amount of sulfur inthe film is desired, at least one ALD cycle, every other ALD cycle, orevery third, fourth, fifth, sixth cycle, etc. could include one or moreadditional sulfur precursor pulses.

In some embodiments, it is desirable to incorporate at least two metalsinto the metal sulfide interface layer. Thus, in an appropriate ALDcycle, one or more cycles may include a pulse of a second, third, orfourth metal in addition to or in lieu of the first metal. For example,in some embodiments, the metal sulfide film comprises aluminum andmagnesium. In some embodiments, the metal sulfide film comprises siliconand magnesium. In some embodiments, the metal sulfide film compriseshafnium and magnesium. For example, pulses of Al and Mg may be used incombination with sulfur precursor pulses to form AlMgS. Similarly, Siand Mg pulses or Si and Hf pulses may be used in combination with sulfurprecursor pulses to form MgSiS or MgHfS, respectively. Without beingtied to any particular, it is believed the use of more than one metalmay achieve particular benefits, such as suppressed crystallization atelevated temperatures, minimized hygroscopic characteristics, and/orenhanced dielectric constants.

Referring again to FIG. 2, which illustrates an exemplary metal sulfidedeposition process 200. Some embodiments may include a pretreatmentprocess at step 201 applied to the substrate surface. A pretreatment maycomprise one or more steps. In the pretreatment, the substrate surfaceon which the metal sulfide is to be deposited may be exposed to one ormore pretreatment reactants and/or to specific conditions, such astemperature or pressure. A pretreatment may be used for any number ofreasons including to clean the substrate surface, remove impurities,remove native oxide, and provide desirable surface terminations. In someembodiments, a pretreatment comprises exposing the substrate surface toone or more pretreatment reactant, such as (NH₄)₂S, H₂S, HCl, HBr, Cl₂,or HF. In some embodiments, a pretreatment process is carried out atabout the same temperature as the subsequent deposition process. In someembodiments, a pretreatment process comprises one or more pulses of asuitable chemical, the pulses ranging from about 0.05 s to about 600 s,preferably from about 0.1 s to about 60 s. In some embodiments, thepressure during a pretreatment process is maintained between about 0.01Torr and about 100 Torr, preferably from about 0.1 Torr to about 10Torr.

In some embodiments, such as where a III-V material is used, HCl may beused as the pretreatment reactant. In some embodiments, such as where agermanium substrate is used, HF may be used as the pretreatmentreactant. In some embodiments, multiple pretreatment reactants are usedsequentially or simultaneously. In some embodiments, a pretreatment mayinvolve multiple applications of one or more pretreatment reactants.

In some embodiments, a pretreatment may comprise first exposing thesubstrate surface to HCl for a period of time and then exposing thesubstrate surface to H₂S for a period of time. Additional steps may alsobe included. For example, in some embodiments, water may be used to washthe substrate surface between the respective HCl and H₂S exposures.Thus, in one possible pretreatment, a suitable substrate surface may beexposed to HCl for a period of between 1 s and 5 minutes, washed withdeionized (DI) H₂O twice for about a period of between about 1 s and 60s, and exposed to two exposures of H₂S for a period of about 1 s toabout 60 s at. The preceding process may occur at any suitabletemperature such as between about 100° C. and about 400° C.

According to some embodiments, a pretreatment may comprise an ex-situwet clean treatment followed by one or more in-situ processes. Thein-situ process may comprise multiple stages with different pretreatmentreactants. For example, one in-situ sequence could comprise alternatingexposure to HCl and H₂S (HCl—H₂S—HCl—H₂S, etc.). Of course, it will berecognized that other combinations or other pretreatment reactants insimilar or different combinations may also be used.

In some embodiments, the substrate surface is pretreated with asulfur-containing compound. In some embodiments, the sulfur-containingcompound may be the same as or different from the sulfur precursor usedin a subsequent metal sulfide deposition process. According to someembodiments, a sulfur-containing pretreatment agent comprises a thiolwith a general formula of R—S—H, wherein R can be an alkane, an alkene,or other carbon-containing group of atoms. In some embodiments, thesulfur-containing pretreatment reactant comprises plasma or radicalsderived from S-containing species. In some embodiments, the pretreatmentagent comprises elemental sulfur. The use of a pretreatment reactantcomprising sulfur may provide —SH terminations on the substrate surface.In such situations, the subsequent exposure to a metal precursor, suchas a magnesium precursor, will result in the immediate formation of Mg—Sbonds and the beginning of a metal sulfide film, such as a MgS thinfilm. In some embodiments, a pretreatment is provided ex situ or in situand may be provided as a liquid bath or by exposure to a vapor phase ofa pretreatment reactant. In some embodiments, the pretreatment processcomprises a sulfur passivation process.

In some embodiments, surface terminations other than S—H terminationsmay be desired. In such instances, it may be desirable to use anon-sulfur-containing pretreatment reactant. For example, in someembodiments, the pretreatment reactant may provide N—H terminations onthe substrate surface. In some embodiments, such pretreatments couldcomprise an NH₃ anneal, N₂ plasma treatment, or exposure to N₂H₄, thoughother methods and other nitrogen-containing compounds may also be used.Similar to the result that may be achieved using sulfur-containingpretreatment reactants, the use of nitrogen-containing reactants mayachieve N—H terminations on the substrate surface.

A pretreatment process may utilize pretreatment reactants in vapor formand or in liquid form. In some embodiments, the pretreatment process maybe carried out at the same temperature and/or pressure as the subsequentdeposition process. In some embodiments, the pretreatment process mayresemble the subsequent deposition process except that the pretreatmentprocess will involve a longer pulse time or exposure time than used inthe subsequent deposition process.

In some specific embodiments, HCl may be used as the pretreatmentchemical and may be used in liquid form and the HCl may diluted (e.g., 1(37%): 10) and may be used in a 1 minute etch. In some specificembodiments, liquid (NH₄)₂S having a concentration of 22% may be used ina 5 minutes dipping process to pretreat the substrate surface. In someembodiments, the duration of the pretreatment process can be variedbroadly without affecting the film properties of the subsequentlydeposited films.

The pretreatment process may be performed at the same temperature and/orpressure as the subsequent ALD process; however, it may also beperformed at a different temperature and/or pressure. In embodimentswhere the pretreatment is performed ex situ, it may be impossible orundesirable to perform the pretreatment at the same temperature and/orpressure as the subsequent ALD process. For example, where apretreatment involves the immersion of the substrate in an aqueoussolution, it may be desirable to allow the pretreatment to proceed at ahigher pressure than the ALD process, which may be performed atrelatively low pressures that could undesirably evaporate thepretreatment reactant.

Referring again to FIG. 2, a first metal reactant or precursor isconducted into the chamber at step 220 in the form of vapor phase pulseand contacted with the surface of the substrate. Conditions arepreferably selected such that no more than about one monolayer of theprecursor is adsorbed on the substrate surface in a self-limitingmanner.

At step 230 excess first reactant and reaction byproducts, if any, areremoved from the reaction chamber, often by purging with a pulse ofinert gas such as nitrogen or argon. Purging the reaction chamber meansthat vapor phase precursors and/or vapor phase byproducts are removedfrom the reaction chamber such as by evacuating the chamber with avacuum pump and/or by replacing the gas inside the reactor with an inertgas such as argon or nitrogen. Typical purging times are from about 0.05to 20 seconds, more preferably between about 1 and 10 seconds, and stillmore preferably between about 1 and 2 seconds. However, other purgetimes can be utilized if necessary, such as when depositing layers overextremely high aspect ratio structures or other structures with complexsurface morphology is needed. The appropriate pulsing times can bereadily determined by the skilled artisan based on the particularcircumstances.

At step 240 a second gaseous, reactant comprising sulfur (also referredto as a sulfur reactant or sulfur precursor) is pulsed into the chamberwhere it reacts with the first reactant bound to the surface. Thereaction forms up to a monolayer of metal sulfide on the substratesurface.

At step 250, excess second reactant and gaseous by-products of thesurface reaction, if any, are removed from of the reaction chamber, asdescribed above for step 230. In some embodiments excess reactant andreaction byproducts are preferably removed with the aid of an inert gas.

The steps of pulsing and purging are repeated at step 260 until a thinfilm of the desired thickness has been formed on the substrate, witheach cycle leaving no more than a molecular monolayer. In some cases, itmight be desirable to achieve at least partial decomposition of at leastone the various precursors.

Additional reactants can also be supplied that, in some embodiments, donot contribute elements to the growing film. Such reactants can beprovided either in their own pulses or along with the metal and/orsulfur precursor pulses. The additional reactants can be used, forexample, to provide a desired surface termination, or to strip or getterligands from one or more of the reactants and/or free by-product.

In some embodiments, additional reactants are used in order tocontribute additional species, such as oxygen or nitrogen, to thegrowing thin film. In some embodiments, the additional reactants may beprovided in the same phase as another precursor, such as during themetal phase or the sulfur phase. In some embodiments, the additionalreactant or reactants constitute their own phase or phases and areprovided separate from both the metal and sulfur phases. Whetherprovided with another phase or separately, the additional reactant(s)may be provided in every cycle, some cycles, or only in one cycle in thedeposition process.

In some embodiments, one or more additional non-metal elements may bedesired in the metal sulfide film, such as nitrogen or oxygen.Additional phases can be incorporated in one or more deposition cycles,or provided after deposition of the metal sulfide film, in order toincorporate such materials. For example, in some embodiments one or morecycles may include a nitrogen phase in which the substrate is exposed toa nitrogen reactant. In some embodiments, the nitrogen phaseincorporates at least some nitrogen into the metal sulfide thin film. Insome embodiments, the nitrogen phase comprises exposing the substratesurface or growing film to N₂ plasma. In some embodiments, the nitrogenphase comprises subjecting the substrate surface or growing film to anannealing process using NH₃. In some embodiments, the nitrogen phasecomprises subjecting the substrate surface or growing film to N₂H₄. Insome embodiments, the nitrogen phase comprises exposing the substrate tonitrogen precursors, nitrogen radicals, atomic nitrogen, nitrogenplasma, or combinations thereof. A nitrogen phase can be included in oneor more deposition cycles by providing a pulse of the nitrogen reactantand purging or after depositing some or all of the complete film. Insome embodiments the nitrogen phase may follow the metal phase or thesulfur phase in one or more deposition cycles.

In some embodiments one or more cycles may include an oxygen phase inwhich the substrate is exposed to an oxygen reactant. In someembodiments, the oxygen phase incorporates at least some oxygen into themetal sulfide thin film. In some embodiments, the oxygen phase comprisesexposing the substrate surface or growing film to oxygen plasma. In someembodiments, the oxygen phase comprises subjecting the substrate surfaceor growing film to an annealing process in an oxygen atmosphere. In someembodiments, the nitrogen phase comprises exposing the substrate tonitrogen precursors, nitrogen radicals, atomic oxygen, oxygen plasma, orcombinations thereof. An oxygen phase can be included in one or moredeposition cycles by providing a pulse of the oxygen reactant andpurging or after depositing some or all of the complete film. In someembodiments the oxygen phase may follow the metal phase or the sulfurphase in one or more deposition cycles.

The metal sulfide thin films of the present disclosure can include anynumber of metals. Accordingly, suitable metal precursors comprising thedesired metal of the metal sulfide can be selected. In some embodimentsa metal sulfide comprising Mg, Ca, La, Sc, Y are formed. In otherembodiments metal sulfides comprising Al, Si, Zn, Cd, Pb, In, Ga, Ge,Gd, Ta, Mo, or W are formed. Appropriate metal sulfides may includethose that exhibit desirable characteristics, such as stability (e.g.,does not reaction with substrate, capping layer, or air), high meltingpoint (e.g., greater than about 1000° C., fewer charge trapping sites(e.g., D_(it)<5e11 1/cm²), and a wide band gap (e.g., >3 eV).

According to some embodiments, a metal sulfide thin film includes two ormore metals. In some embodiments, additional deposition phases are addedto one or more deposition cycles to incorporate the additional metal ormetals. The additional metal phase(s) may follow the first metal phaseor follow the sulfur phase. In some embodiments two or more differentmetal precursors may be provided simultaneously in the same metal phaseof a deposition cycle. In some embodiments metal precursors comprisingdifferent metals may be used in different deposition cycles. Forexample, a first metal precursor may be the only metal precursor used inone or more deposition cycles and a second metal precursor comprising asecond, different metal, may be used in one or more other depositioncycles.

And in some films having two or more metals, additional non-metals otherthan sulfur, such as oxygen or nitrogen, may also be included. Again,additional deposition phases may be added to one or more depositioncycles to incorporate the additional materials. Accordingly, it ispossible to achieve metal sulfide thin films with two or more metals,sulfur, and nitrogen or metal sulfide thin films with two or moremetals, sulfur, and oxygen. Examples include, but are not limited to,MgHfOS, MgHfS, MgSiS, AlMgS, MgSO, and MgSN.

In some embodiments, the additional elements may already comprise a partof either the metal precursor or the sulfur precursor. For example,either the metal or sulfur precursor may include oxygen or nitrogen,which could serve as the additional desirable component in the resultingmetal sulfide film. Where one or both of the metal and sulfur precursorsalso includes the additional element, it may be desirable to use thatparticular precursor in all or only some of the deposition cycles. Forexample, if the sulfur precursor includes the additional desirableelement, such as oxygen, then that precursor could be used for only oneor some of the deposition cycles while a different,non-oxygen-containing sulfur precursor is used for the remaining cycles.

In some such embodiments, the deposition may be performed as a two-stepprocess, such as when forming a metal oxysulfide thin film. Thus, thefirst step may involve the formation of a metal sulfide film, and thesecond step may involve the formation or modification of the metalsulfide film into a metal oxysulfide film.

Similarly, a two-step process may be used to incorporate othermaterials, such as nitrogen, into the metal sulfide film. For example,the first step may involve the formation of a metal sulfide film, andthe second step may involve the exposure of the metal sulfide film to anitrogen precursor or a nitrogen-rich atmosphere so as to incorporate atleast some nitrogen in to the film.

MgS has been chosen as an exemplary metal sulfide for the sake of thisdisclosure. In some embodiments, the magnesium precursor is providedfirst in an ALD cycle for forming MgS. After forming an initial surfacetermination, if necessary or desired, a first magnesium precursor pulseis supplied to the workpiece. In accordance with some embodiments, thefirst precursor pulse comprises a carrier gas flow and a volatilemagnesium species that is reactive with the workpiece surfaces ofinterest. Exemplary magnesium precursors include magnesiumbeta-diketonates and cyclopentadienyl-based (“Cp”) precursors, such asMgCp₂, which is desirable because of its high volatility and reactivity.Accordingly, the magnesium precursor adsorbs upon the workpiecesurfaces. In some embodiments, the reaction is self-limiting such thatthe first precursor pulse self-saturates the workpiece surfaces suchthat any excess constituents of the first precursor pulse do not furtherreact with the molecular layer formed by this process.

The first metal precursor pulse is preferably supplied in gaseous form.The metal precursor gas is considered “volatile” for purposes of thepresent description if the species exhibits sufficient vapor pressureunder the process conditions to transport the species to the workpiecein sufficient concentration to saturate exposed surfaces.

In some embodiments the metal precursor pulse is from about 0.01 secondsto about 60 seconds, from about 0.02 seconds to about 30 seconds, fromabout 0.025 seconds to about 20 seconds, from about 0.05 seconds toabout 5.0 seconds, about 0.05 seconds to about 2.0 seconds or about 0.1seconds to about 1.0 second.

After sufficient time for a molecular layer to adsorb on the substratesurface, excess first precursor is then removed from the reaction space.In some embodiments the excess first precursor is purged by stopping theflow of the first chemistry while continuing to flow a carrier gas orpurge gas for a sufficient time to diffuse or purge excess reactants andreactant by-products, if any, from the reaction space. In someembodiments the excess first precursor is purged with the aid of oxygengas, or another purge gas, that is flowing throughout the ALD cycle.

In some embodiments, the first precursor is removed from the reactionspace, which may involve a purge gas that flows for about 0.05 to 20seconds, more preferably between about 1 and 10 seconds, and still morepreferably between about 1 and 2 seconds.

In the second phase, a sulfur precursor is provided to the reactionspace. The adsorbed first reactant may then react with the sulfurprecursor to form magnesium sulfide. In some embodiments the sulfurprecursor pulse is from about 0.01 seconds to about 60 seconds, fromabout 0.02 seconds to about 30 seconds, from about 0.025 seconds toabout 20 seconds, from about 0.05 seconds to about 5.0 seconds, about0.05 seconds to about 2.0 seconds or about 0.1 seconds to about 1.0second. However, depending on the reactor type, substrate type and itssurface area, the sulfur precursor pulsing time may be even higher than10 seconds. In some embodiments, pulsing times can be on the order ofminutes. The optimum pulsing time can be readily determined by theskilled artisan based on the particular circumstances.

The concentration of the sulfur precursor in the reaction chamber may befrom about 0.01% by volume to about 99.0% by volume. And the sulfurprecursor may flow through the reaction chamber at a rate of betweenabout 1 standard cm³/min and about 4000 standard cm³/min.

In some embodiments, the growth rate of the metal sulfide material isbetween about 0.01 Å/cycle and about 2.0 Å/cycle. In some embodiments,the growth rate is between about 0.1 Å/cycle and about 1.0 Å/cycle. Insome embodiments, the growth rate is about 0.2 Å/cycle.

The metal sulfide ALD processes of the present disclosure comprise oneor more cycles. Some embodiments involve the repetition of at leastabout 5 cycles, at least about 10 cycles, or at least about 50 cycles.In some embodiments, no more than 100 cycles are performed to form athin film of a desirable thickness.

After a time period sufficient to completely react the previouslyadsorbed molecular layer with the sulfur precursor, for example thesulfur precursor pulse, any excess reactant and reaction byproducts areremoved from the reaction space. As with the removal of the firstreactant, this step may comprise stopping the flow of the sulfurprecursor and continuing to flow a carrier gas, for a time periodsufficient for excess reactive species and volatile reaction by-productsto diffuse out of and be purged from the reaction space. In someembodiments a separate purge gas may be used. The purge may, in someembodiments, be from about 0.1 to about 10 s, about 0.1 to about 4 s orabout 0.1 to about 0.5 s. Together, the sulfur precursor provision andremoval represent a second phase in a metal sulfide ALD cycle, and canalso be considered a sulfur or sulfide phase.

The two phases together represent one ALD cycle, which is repeated toform metal sulfide layers, such as magnesium sulfide layers. While theALD cycle is generally referred to herein as beginning with the metalphase, it is contemplated that in other embodiments the cycle may beginwith the sulfur phase. As mentioned above, providing a sulfur precursorfirst may also serve to pretreat the substrate surface. Thus, in someembodiments, the substrate is subjected to a pretreatment where thepretreatment reactant is the same as the sulfur precursor.

The metal precursor employed in the ALD type processes may be solid,liquid, or gaseous material under standard conditions (room temperatureand atmospheric pressure), provided that the metal precursor is in vaporphase before it is conducted into the reaction chamber and contactedwith the substrate surface.

In some embodiments, the sulfur precursor includes sulfur plasma orsulfur radicals. In such embodiments, the sulfur may be energized withinthe reaction chamber or upstream of the reaction chamber. Where a plasmais desired, the flow of un-energized sulfur precursor may comprise atype of purge gas, such that after the substrate has been exposed to asulfur plasma for a desired period of time, the plasma generator may beturned off and the flow of sulfur precursor itself is used to clear thereaction chamber of excess sulfur plasma and unreacted byproducts.

While one skilled in the art will recognize that any number of suitablesulfur precursors may be used, appropriate sulfur precursors includesulfur-containing compounds that favorably react with the ligands or apreviously or subsequently deposited metal precursor. Accordingly,selection of an appropriate sulfur precursor may depend on the specificmetal precursor used and the nature of the ligands in the metalprecursor. In some embodiments, the metal precursor is MgCp₂, and thesulfur precursor is either H₂S or (NH₄)₂S.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature, as discussed above. Thepreferred deposition temperature may vary depending on a number offactors, such as, and without limitation, the reactant precursors, thepressure, flow rate, the arrangement of the reactor, and the compositionof the substrate including the nature of the material to be depositedon.

FIG. 3 illustrates an example of an ALD process for forming a magnesiumsulfide thin film according to some embodiments of the presentdisclosure. A magnesium sulfide ALD process comprises multiple stepsthat may occur in the order shown or may be rearranged as explained infurther detail below. According to some embodiments, a magnesium sulfidethin film is formed by an ALD-type process 300 comprising multiplepulsing cycles, each cycle comprising:

-   -   pulsing a vaporized first Mg precursor into the reaction chamber        at step 320 to form at most a molecular monolayer of the Mg        precursor on the substrate,    -   purging the reaction chamber at step 330 to remove excess Mg        precursor and reaction by products, if any,    -   providing a pulse of a second sulfur precursor onto the        substrate at step 340,    -   purging the reaction chamber at step 350 to remove excess second        reactant and any gaseous by-products formed in the reaction        between the Mg precursor layer on the first surface of the        substrate and the second reactant, and    -   repeating at step 360 the pulsing and purging steps until a        magnesium sulfide thin film of the desired thickness has been        formed.

According to some embodiments, ALD process 300 may be preceded by apretreatment of the substrate at step 310. In some embodiments, thepretreatment reactant may comprise sulfur, and in some embodiments, thesulfur-containing pretreatment reactant may be the same as the sulfurprecursor utilized in step 340.

According to some embodiments, the metal sulfide film comprises at leastsome oxygen. Such oxygen may be present because at least one of theprecursors contains oxygen or because of a compound used with theprecursor contains oxygen, such as H₂O in an aqueous solution ofammonium sulfide. However, in some embodiments, the presence of oxygenis undesirable. Hence, the amount of oxygen in the thin film will bekept to a minimum or will not be present in any appreciable amount. And,in some embodiments, precursors having no or essentially no oxygen areutilized.

A capping layer may be desirable in some embodiments, for examplebecause some metal sulfide thin films are hygroscopic. Thus, accordingto some embodiments, a capping layer is deposited or formed on top ofthe metal sulfide thin film. In some embodiments, a subsequentlydeposited or formed dielectric layer serves as a capping layer. In someembodiments the capping layer may protect the thin film during transportof the substrate.

In some embodiments, the metal sulfide thin film is subjected to a postdeposition treatment process. In some embodiments, the post treatmentprocess is used subsequent to forming a dielectric layer above theinterface layer. However, in some embodiments, a pretreatment is carriedout prior to any subsequent deposition, such as the deposition of acapping layer. In some embodiments, a post deposition treatment processincludes, for example, at least one of an annealing process, a forminggas annealing process, and a sulfur passivation process. A sulfurpassivation process may remove at least some unbound or undesirablecarbon that may be present in the metal sulfide thin film or the cappinglayer (e.g., the dielectric layer) on top of the metal sulfide thinfilm. H₂S may be used in a suitable sulfur passivation process asdescribed in greater detail below.

Metal Precursors

It will be understood by one skilled in the art that the metal of themetal sulfide thin films of the present disclosure may be selected fromany number of options. In some embodiments, the metal precursor isselected from compounds containing Be, Mg, Ca, Ba, Sr, Y, Sc, La andother lanthanides (i.e., Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, and Lu). In some embodiments, the metal precursor is selected fromcompounds containing Al, Si, Zn, Cd, Pb, In, Ga, Ge, Gd, Ta, Mo, or W.In some embodiments, the metal precursor comprises one or more ligands,such as cyclopentadienyl (“Cp”) ligands. MgCp₂ is one example of asuitable metal precursor. In some embodiments, the metal precursor is ametal beta-diketonate. In some embodiments, the metal precursor is not acyclopentadienyl-compound of Ba or Sr. In some embodiments, the metalprecursor is not a cyclopentadienyl-compound of Ce or Mn.

In some embodiments, the metal precursor has the following formula:ML₂A_(x)  (I)

wherein each L can be independently selected to be a hydrocarbon groupand M can be is Be, Mg, Ca, Ba or Sr and A can be neutral ligand oradduct, such as ethylenediamine or EtOH, and x can be from 0 to 2.Preferably L can be linear, branched, cyclic alkyl or unsatureatedhydrocarbon group, such as alkenyl, alkynyl, aromatic, cyclopentadienyl,phenyl, cyclooctadienyl, or cycloheptatrienyl group. Preferably M is Mgor Ca. Preferably x is 0. More preferably L is cyclopentadienyl group.More preferably M is Mg. In some embodiments, the L can be a bidentateligand, such as betadiketonate, guanidinate or amidinate. In someembodiments, the betadiketonate ligand can be acetylacetonate or2,2,6,6-tetramethyl-3,5-heptanedionato (thd).

In some embodiments, the metal precursor is a cyclopentadienyl compoundor derivated thereof, such as alkylsubstituted cyclopentadienyl compoundand have the following formula:M(R₁R₂R₃R₄R₅Cp)₂  (II)

-   -   wherein each of the R₁-R₅ can be independently selected to be        hydrogen or substituted or unsubstituted alkyl group and M can        be is Be, Mg, Ca, Ba or Sr. In preferred embodiments the M is Mg        and each of the R₁-R₅ can be independently selected to be R₁-R₅        can be hydrogen or linear or branched C₁-C₅ alkyl group. In more        preferred embodiments the M is Mg and each of the R₁-R₅ can be        independently selected to be hydrogen or C₁-C₃ alkyl group, such        as methyl, ethyl, n-propyl or i-propyl group. In most preferred        embodiment the precursor is Mg(Cp)₂.

In preferred embodiments, the metal M in formulas is Mg, Ca, Sc, Y orLa. In more preferred embodiments, the metal in the formula is Mg.

In some embodiments, the metal precursor comprises one or more ligands,such as cyclopentadienyl (“Cp”) ligands. These source compounds can beselected from a group consisting of the following compounds:(Cp)_(x)M  (III);(Cp)_(x)L_(y)M  (IV);(Cp)_(x)W_(n)M  (V);(CP)_(x)L_(y)W_(n)M  (VI);

-   -   wherein M is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,        Tm, Yb or Lu;    -   Cp is a cyclopentadienyl or a cyclooctadienyl group, so that Cp        groups in chemical formulas I—IV can be the same with each other        or different from one other; x denotes the number of the Cp        ligands and it is an integer from 1 up to the oxidation state of        M;    -   L_(y) is a neutral adduct ligand that bounds from one or more of        its atoms to the rare earth metal and where y denotes the number        of the bound ligands; and    -   W is some other ligand with a valence of −1 than Cp and where n        denotes the number of the ligands. W is preferably        beta-diketonate or its corresponding sulfur or nitrogen        compound, halide, amide, alkokside, carboxylate or Schiff s        base. It must be noted that cyclooctadiene is usually shortened        as Cod, but here the presentation is simplified by the use of        the single common abbreviation Cp for both cyclopentadienyl and        cyclooctadienyl.

In the chemical equations I-IV, the cyclopentadienyl and/orcyclooctadienyl groups can be in the same molecule, so that there is abridge between two Cp-groups consisting of a substituted orunsubstituted C₁-C₆ chain that may contain a heteroatom selected fromSi, N, P, Se, S or B.

L is preferably

-   -   (i) a hydrocarbon,    -   (ii) a hydrocarbon that contains oxygen,    -   (iii) a hydrocarbon that contains nitrogen,    -   (iv) a hydrocarbon that contains sulfur,    -   (v) a hydrocarbon that contains phosphor,    -   (vi) a hydrocarbon that contains arsenic,    -   (vii) a hydrocarbon that contains selenium and/or    -   (viii) a hydrocarbon that contains tellurium

L is more preferably

-   -   (a) amine or polyamine,    -   (b) bipyridine,    -   (c) a ligand according to a chemical equation

-   -   wherein G is —O—, —S—, or —NR¹, where R¹ is hydrogen or        substituted or unsubstituted, cyclic, linear or branched, alkyl,        alkenyl, aryl, alkylaryl, arylalkyl, alkoxy, thio, cyano or        silyl group. A cyclic or aromatic ring in R¹ may contain a        heteroatoin. Hydrogen or R¹-type substituent may also be        attached to the carbon atoms in chemical equation V, or    -   (d) ether or thioether.

Cyclopentadienyl or cyclooctadienyl group Cp in chemical formulas I-IVhas a form:Cp′R_(m)H_(a-m)  (VII)

-   -   wherein m is an integer 0-8, when a is 8 and m is an integer 0-5        when a is 5,    -   Cp′ is fusioned or isolated cyclopentadienyl or cyclooctadienyl        and    -   R is a hydrocarbon fragment continuing 1-20 carbon atoms,        preferably C₁-C₆ hydrocarbon.

R ligands can be the same with each other or different from one other. Rcan be a substituted or unsubstituted, cyclic, linear or branched, alkylalkenyl, aryl, alkylaryl, arylalkyl, alkoxy, tbio, amino, cyano or silylgroup. The cyclic or aromatic ring of the substituent may contain ahetero atom. Examples of the substituents are methyl, ethyl, propyl andisopropyl groups.

Neutral adduct ligands L shown in chemical equations II and IV can beethers, amines or solvent molecules such as tetrahydrofurane that form abond to the metal with one atom. Examples of suitable neutral adductligands that form a bond to a metal with several atoms are polyethersand polyamines.

In some embodiments, it is desirable to have the metal in the metalsulfide thin film be the same as the metal in a dielectric layer that isto be deposited over the metal sulfide layer. Thus, in some embodiments,a metal precursor is selected that has the same metal. In someembodiments the precursor may be the same precursor that is used in asubsequent process to deposit a dielectric layer, such as a metal oxide.In this vein, in some embodiments, the metal is selected from metaloxides that are desirable dielectric or high-k materials, such as MgO,SrTiO_(x), and BaTiO_(x).

Where a specific metal oxide is known to serve as a suitable or gooddielectric material, the metal precursor used to form the metal oxidemay be used in the presently disclosed methods to form a desirable metalsulfide interfacial layer.

In some embodiments, the metal precursor does not comprise cesium.However, cesium may comprise a component of the metal precursor in otherembodiments. In some embodiments, the metal precursor does not comprisestrontium and/or barium. However, strontium and/or barium may comprise acomponent of the metal precursor in other embodiments. In someembodiments, the metal precursor does not comprise calcium.

In some embodiments, the metal precursor is selected such that the metalof the metal precursor is distinct from any metal that may be present inthe underlying substrate. For example, the metal precursor may beselected so as to provide a metal that is distinct from a metal in anunderlying high-mobility channel. Thus, in some embodiments, the metalprecursor specifically does not comprise Ga, As, In, Sb, etc. dependingon the type of high-mobility channel or underlying substrate that isused. Similarly, in some embodiments, the metal precursor is selectedsuch that the metal of the metal precursor is distinct from any metalthat may be present in the high-k material or dielectric layer formedabove the interfacial layer. However, in some embodiments, the metal ofthe metal precursor may also be found in one or both the underlyinghigh-mobility channel and the overlying high-k material or dielectriclayer.

According to some embodiments where the formation of a metal oxysulfideor metal oxysulfate thin film is desired, suitable metal precursors caninclude, for example, compounds containing Mg, Al, In, Ga, Ge, and Gd.

Sulfur Precursors

It will be understood by one skilled in the art that any number ofsulfur precursors may be used. In some embodiments, the sulfur precursoris selected from the following list: H₂S, (NH₄)₂S, dimethylsulfoxide((CH₃)₂SO), elemental or atomic S, other precursor containing S—H bond,such as H₂S₂ or such as thiols R—S—H, wherein R can be substituted orunsubstituted hydrocarbon, preferably C₁-C₈ alkyl group, more linear orbranched preferably C₁-C₅ alkyl group. Suitable sulfur precursors mayinclude any number of sulfur-containing compounds so long as theyinclude at least one S—H bond. In some embodiments, the sulfur precursormay comprise a sulfur plasma or sulfur radicals. In some embodimentswhere energized sulfur is desired, a plasma may be generated in thereaction chamber or upstream of the reaction chamber.

In some embodiments where (NH₄)₂S is employed, the (NH₄)₂S may beprovided in an aqueous solution. In such embodiments, it may bedesirable to provide the sulfur precursor in shorter pulses so as toreduce the effects that H₂O vapor from the solution may have on thesubstrate or film growth. However, in some embodiments, the sulfurprecursor itself may comprise oxygen.

According to some embodiments, it is desirable to use anoxysulfide—generically described as O_(x)S_(y)— or anoxysulfate—generically described as O_(x)(SO₄)_(y). In some embodiments,an aqueous solution of SO_(x), such as SO₄, may be used as the sulfurprecursor.

Integration

The metal sulfide thin films of the present disclosure may be used in avariety of semiconductor applications. For example, metal sulfide filmsmay be particularly useful in high-mobility channel applications, suchas where III-V materials or germanium substrates are used. High-mobilitychannels are generally desirable in high-speed applications orhigh-switching applications. Metal sulfide films may be used, forexample, in FinFETs, planar transistors, MOSFETs, capacitors, verticalnanowires, and power transistors.

FIG. 4 illustrates an exemplary process flow 400 for the formation of athree-dimensional structure, such as a gate stack, capacitor, etc. Insome embodiments, the formation of a suitable semiconductor structureproceeds as follows:

-   -   A suitable substrate, such as one having a high-mobility channel        (e.g., InGaAs), is provided at step 410;    -   The substrate is optionally subjected to a pretreatment process        either ex situ or in situ at step 420;    -   A suitable metal sulfide thin film is formed on a surface of the        substrate, such as by an ALD process, at step 430;    -   A capping layer (e.g., a dielectric, such as a high-K dielectric        like Al₂O₃ or HfO₂) is formed over the metal sulfide thin film        at step 450;    -   The substrate is optionally subjected to a post deposition        treatment process, either before or after formation of the        capping layer, at step 460;    -   Optionally, a barrier layer, such as TiN, is formed at step 470        over the capping layer by a process such as an ALD process;    -   A metal gate is then formed at step 480 on top of the previously        formed layers; and    -   Any further layers or materials as desired are formed on top of        the metal gate in subsequent processing steps at step 490.

According to some embodiments, the substrate surface provided at step410 will include a high-mobility channel. Exemplary high-mobilitychannels include those composed of InGaAs and similar III-V materials.The substrate surface may have been subject to prior processing beforebeing provided for the metal sulfide film integration process 400. Forexample the substrate may have been subjected to a doping process toform a source or a drain or both.

According to some embodiments, process 400 will be used to form athree-dimensional architecture, such as a transistor, a FinFET, verticalnanowire transistors, a planar transistor, a capacitor, a powertransistor, etc. A substrate is provided in step 400. In someembodiments the substrate is placed into a reaction space that is partof a deposition reactor, such as an ALD reactor, where the metal sulfideinterface film will be deposited. In some embodiments the substrate isprovided to a tool for a pretreatment process 420 and subsequentlyprovided to a deposition reactor.

FIG. 4 illustrates an optional pretreatment at step 420. A pretreatmentmay be used for any number of reasons including to clean the substratesurface, remove impurities, remove native oxide, and/or providedesirable surface terminations. In some embodiments, the pretreatmentreactant comprises any suitable reducing chemistry. In some embodiments,a pretreatment comprises exposing the substrate surface to pretreatmentreactant, which may comprise, for example, (NH₄)₂S, H₂S, HCl, or HF. Theappropriate pretreatment reactant may be selected by the skilled artisanbased on the particular circumstances and desired effect.

In some embodiments, such as where the substrate comprises a III-Vmaterial, HCl may be used as the pretreatment reactant. An HCl dip mayremove the surface contaminants, such as hydrocarbons, particles andmetals, but not fully remove the native oxide. HCl concentration mayvary, but not limited, from to concentrated about 37 weight-% to dilute1 weight-%.

In some embodiments, such as where a germanium substrate is used, HF maybe used as the pretreatment reactant. HF dip may remove the surfacecontaminants, such as hydrocarbons, particles and metals, but not fullyremove the native oxide. HCl concentration may vary, but not limited,from to concentrated about 50 weight-% to dilute 0.1 weight-%.

In some embodiments, a pretreatment process will utilize both HCl andHF. For example, a substrate surface may be exposed first to an HClsolution and then to an HF solution or vice versa. In some embodiments,the pretreatment process comprises a sulfur passivation process. In someembodiments the substrate is exposed to a pretreatment reactantcomprising sulfur. The use of a pretreatment reactant comprising sulfurmay provide —SH terminations on the substrate surface. In suchsituations, the subsequent exposure to a metal precursor in thebeginning of step 430, such as a magnesium precursor, will result in theimmediate formation of metal-sulfur bonds and the beginning of the metalsulfide interface layer. In some embodiments, a pretreatment process maycomprise the substrate surface being exposed to H₂S.

In some embodiments, surface terminations other than —SH terminationsmay be desired. In such instances, it may be desirable to use anon-sulfur-containing pretreatment reactant, such as the HF or HClexposure described above. According to some embodiments, HCl and/or HFmay be applied in-situ or in a clustered configuration.

Pretreatment 420 may comprise exposure to a liquid reactant, such as bysubmerging the substrate in a liquid bath or by exposing the substrateto a vapor phase pretreatment reactant. In some cases in-situ HCl or HFpretreatment from gas phase is done without airbreak or exposure to air.In some cases in-situ H₂S pretreatment from gas phase is done withoutairbreak or exposure to air.

In some embodiments, pretreatment may comprise changing the temperatureand atmosphere, such as hydrogen plasma treatment, NF₃ plasma treatment,or thermal H₂ bake.

Subsequent to the pretreatment step, if performed, a metal sulfideinterface layer is formed 430. In some embodiments, a suitable interfacelayer is one that comprises a metal sulfide. Suitable metal sulfidesincludes those where the metal is selected from the following: Be, Mg,Ca, Ba, Sr, Y, Sc, La and other lanthanides (i.e., Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), Al, Si, Zn, Cd, Pb, In, Ga, Ge,Gd, Ta, Mo, and W. In some embodiments, suitable metal sulfides includesthose where the metal is not selected from the following: Al, Ga, or In.In some embodiments, it is desirable that the metal of the metal sulfidefilm be distinct from the metal of either or both the underlyingsubstrate surface and an overlying layer, such as a subsequently formedcapping layer or dielectric layer. In some embodiments, the interfacelayer is deposited to be a distinct layer from the substrate meaningthat no material from the substrate is consumed for the interface layer,except that some bonds may form between the substrate and the interfacelayer.

In some embodiments, the metal sulfide thin film is deposited to achievea particular thickness. Suitable thicknesses may be greater than orequal to about 1 Å and less than or equal to about 50 Å. In someembodiments, the thickness will be between about 5 Å and about 30 Å. Insome embodiments, the thickness will be between about 5 Å and about 15 Åor 10 Å. In some embodiments, the thickness is between about 1 Å andabout 5 Å. In to some embodiments, the suitable thickness will be onethat achieves a complete layer over the substrate surface (i.e., onethat leaves no gaps). Accordingly, the actual thickness that achieves acomplete layer may depend on the type of metal sulfide formed and thetypes of precursors used to achieve the metal sulfide.

In some embodiments, suitable metal sulfide materials include one ormore of the following: beryllium sulfide (BeS), magnesium sulfide (MgS),calcium sulfide (CaS), barium sulfide (BaS), strontium sulfide (SrS),yttrium sulfide (Y₂S₃), lead sulfide (PbS), indium sulfide (In₂S₃),gallium sulfide (Ga₂S₃), aluminum sulfide (Al₂S₃), silicon sulfide(SiS₂), zinc sulfide (ZnS), cadmium sulfide (CdS), germanium sulfide(GeS₂), tantalum sulfide (TaS₂), molybdenum sulfide (MoS₂), lanthanumsulfide (LaS) and other sulfides of lanthanides (such as gadoliniumsulfide (Gd₂S₃)), tungsten sulfide (WS₂), hafnium sulfide (HfS_(x)),zirconium sulfide (ZrS_(x)), titanium sulfide (TiS_(x)), and mixturesthereof. Other metal sulfides are also possible. For simplicity, thesemetal sulfides have been indicated to have these generalstoichiometries. But it will be understood that the exact stoichiometryof any given metal sulfide will vary based on the oxidation state of themetal. Accordingly, other stoichiometries are expressly contemplated.

In some embodiments the metal sulfide interface layer comprises Al₂S,SiS₂, ZnS, CdS, SrS, CaS, BaS, PbS, In₂S₃, Ga₂S₃, GeS₂, Gd₂S₃, TaS₂,MoS₂ or WS₂. In some embodiments the metal sulfide interface layer is aMgS layer. In some embodiments, the metal sulfide further comprisesoxygen and nitrogen as well as optionally additional metals, such as inMgHfOS, MgHfS, MgSiS, AlMgS, MgSO, and MgSN.

In some embodiments, the deposited metal sulfide interface comprises atleast about 5 at-% of sulfur, preferably more than about 15 at-% ofsulfur and more preferably more than about 30 at-% of sulfur and mostpreferably more than about 40 at-% of sulfur. Depending on the metaloxidation state the metal sulfide interface may comprise sulfur fromabout 45 at-% to about 75 at-%.

In some embodiments, the metal sulfide interlayer is formed by an ALDprocess as described above. In some embodiments, the metal sulfide isformed by a CVD process. CVD-like processes or a combination of ALD andCVD processes may also be used. In some embodiments, other processes,such as PVD, PEALD, etc. may be used.

In some embodiments the metal sulfide interface layer can be subjectedto a post-deposition treatment 440 prior to formation of a capping layer450. For example, once a desired thickness of the metal sulfide layer430 is achieved, a sulfur passivation process (or other suitable postdeposition treatment, such as an annealing process or a forming gasannealing process) may be carried out, after which a capping layer maybe formed over the treated interface layer.

Subsequent to any post deposition treatment processing, a capping layermay be formed over the metal sulfide interface layer. A capping layermay be desirable in some embodiments, for example because some metalsulfide thin films are hygroscopic. Thus, according to some embodiments,a capping layer is deposited or formed on top of the metal sulfide thinfilm. In some embodiments, a subsequently deposited or formed dielectriclayer serves as a capping layer. In some embodiments the capping layermay protect the thin film during transport of the substrate.

In some embodiments the capping layer 450 may be a dielectric layer. Insome embodiments the capping layer is deposited and a separatedielectric layer is deposited over the capping layer, where thedielectric layer comprises a different material from the capping layer.For example, in some embodiments, a capping layer comprising a metalsulfide or metal oxysulfide having a different metal from the one usedin interface layer 430 is deposited over interface layer 430 prior todepositing a dielectric or high-k material.

The capping layer formed at step 450 may comprise a dielectric layer.Generally, the dielectric layer includes a high-k material, such asaluminum oxide, tantalum oxide, hafnium oxide, or titanium oxide. Insome embodiments, the capping layer may comprise a non-high-k material.As with the interface layer, the capping layer may be formed by ALDprocesses, CVD process, etc. The capping layer may have a thickness offrom about 5 Å to about 200 Å, preferably from about 7 Å to about 100 Å,more preferably from about 10 Å to about 80 Å. The specific material andthickness can be selected by the skilled artisan based on the particularcircumstances, including the specific type of structure being formed. Insome embodiments, if the device has to have a high breakdown voltage,like in the case of power devices, the dielectric capping layer may havea thickness up to 100 nm to achieve desired properties.

A post-deposition treatment step 460 may be performed after theformation of the capping layer at step 450. In some embodiments, thepost deposition treatment may precede the formation of a capping layer.In some embodiments where the capping layer is not a dielectric layer, apost deposition treatment may be applied after the formation of thecapping layer but before the formation of a dielectric layer. In otherembodiments the post deposition treatment step may be carried out afterformation of a dielectric layer.

Similar to the pretreatment optionally applied at step 420, the postdeposition treatment may involve the exposing the previously formedlayers to specific conditions and/or reactants in order to improve theproperties of the deposited films. For example, a post depositiontreatment step may serve to remove unreacted reactants or reactionby-products, and/or to remove undesirable impurities from the depositedlayer or layers. The post deposition treatment step may also change thephysical properties of the deposited layers. In some embodiments, a postdeposition treatment process may include, for example, an annealingprocess, for example annealing in a forming gas atmosphere, or apassivation process. The passivation may remove at least some unbound orundesirable carbon that may be present in the metal sulfide thin film orthe capping layer (e.g., the dielectric layer) on top of the metalsulfide thin film.

A suitable post deposition treatment may involve an anneal in a specificatmosphere performed at temperatures from about 300° C. to about 800°C., pressures from about 0.1 Torr to about 760 Torr, and a forming gasN₂/H₂ or N₂ atmosphere. According to some embodiments, the use of a postdeposition process may incorporate additional elements in the depositedmaterials. For example, in some embodiments, the use of a postdeposition treatment involving a nitrogen precursor may result in theincorporation of nitrogen into the either or both the metal sulfide thinfilm and the capping layer. Similarly the use of a post depositionprocess involving oxygen may result in the incorporation of at leastsome oxygen into the metal sulfide thin film.

Following any post deposition treatment, an optional barrier layer maybe formed 470. Suitable materials for a barrier layer may includeelemental metal, metal nitrides, silicon-doped metal nitrides, metalboron carbides, metal aluminum carbides, metal aluminum siliconcarbides, metal boron silicon carbides, carbides, and carbonitrides ofvarious metals, such as titanium, tantalum, etc., and mixtures thereof.Suitable examples include SiN, TaCN, TiSiN, and TaSiN. In the case ofmetal carbides, suitable metals include Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,and W with Ti or Ta being the most preferable options in someembodiments. In some embodiments the barrier layer might also be anoxide, such as Al₂O₃, MgO or La₂O₃, which can help in tuning theproperties of the device, such as the effective work function of themetal gate in the device. As with the previous layers, the barrier layermay be formed by ALD processes, CVD process, etc.

At step 480, a gate is formed. In some embodiments the gate is a metalgate. The gate may be formed by any process known in the art, such as byan ALD process, a CVD process, etc. The metal gate may comprise anynumber of materials, such as TiN, TiC, TiAlC, TaC, TaAlC, NbAlC, TiAl,Al, TaAl, Ta, TaN, TaCN, W, WN, TiWN, and Co. In some embodiments,suitable metals for use in the metal gate materials include Ti, Zr, Hf,V, Nb, Ta, Cr, Mo, and W and nitrides, silicon-doped nitrides, boroncarbides, aluminum carbides, aluminum silicon carbides, boron siliconcarbides, carbides, and carbonitrides of those metals.

In some embodiments, a process such as the one outlined above, isperformed in situ or in a cluster tool. In some embodiments, only themetal sulfide formation and capping layer formation are performed insitu. In some cases, the presence of the capping layer allows for thesubstrate to be more easily transferred between tools.

In some embodiments, subsequent processing may occur after the formationof the metal gate. For example, additional layers may be formed orpatterning of the deposited layers may occur. In some embodiments, theprocess is used to form a three dimensional structure, such as a fin ina FinFET device

EXAMPLE 1

A number of metal sulfide films were formed using an ALD process inwhich process conditions were varied. The metal chosen for the metalsulfide was magnesium and precursor was Mg(Cp)₂, and the sulfurprecursor was (NH₄)₂S extracted from a bubbler containing (NH₄)₂Ssolution in water. The metal and sulfide reactants or precursors werepulsed through a reaction space in an ALD process with pulse timesranging from 40 ms to 50 ms. Growth rates varied between about 0.2Å/cycle and about 0.5 Å/cycle were observed with the faster growth ratesoccurring initially and the growth rate slowing to a steady 0.2 Å/cycle.The reaction temperature was varied from about 250° C. to about 300° C.

The resulting films were analyzed using XRR analysis, which determined aMgS density of about 2.6 g/cm³. This is within the range of bulk MgSdensity (2.6-2.8 g/cm³). It was also determined by XRD analysis that apulsing time for the sulfur precursor of about 50 ms achieved anMgS-dominated film and that a pulsing time of about 1000 ms achieved aMgO-dominated film. Almost pure films of MgS formed at very shortexposure (pulse) times. As the exposure (pulse) time was increased,oxygen was incorporated into the film forming MgS_(x)O_(1-x) to thelimit for very long exposure (pulse) times where the film is almost pureMgO.

Based on the results of this experiment, it was determined that suitablereaction condition would include the following: reaction temperaturefrom about room temperature (e.g., 18° C.) to about 400° C., morepreferably from about 50° C. to about 375° C., and most preferably fromabout 100° C. to about 350° C.; pulse time of between about 0.025seconds to about 60 seconds; pressure ranging from about 0.5 Torr toabout atmospheric pressure (i.e., 760 Torr); and a sulfur precursorprovided in either vapor or liquid form.

EXAMPLE 2

A number of metal sulfide films were formed using an ALD process inwhich process conditions were varied. Prior to film formation, thesubstrates were subjected to a pretreatment process comprising exposureto HCl and H₂S. The metal chosen for the metal sulfide was magnesium,and the precursor was Mg(Cp)₂, and the sulfur precursor was H₂S. Themetal and sulfide reactants or precursors were pulsed through a reactionspace in an ALD process with pulse times ranging from about 50 ms toabout 3 s. Growth rates varied between about 0.2 Å/cycle and about 0.5Å/cycle with the faster growth rates occurring initially and the growthrate slowing to a steady 0.2 Å/cycle. The reaction temperature was about250° C. After deposition was complete, the films were subjected to apost deposition treatment comprising exposure to gas mixture of N₂ andH₂ at 400° C. The resulting films were analyzed using XRR analysis,which determined a MgS density of about 2.6 g/cm³. This is within therange of bulk MgS density (2.6-2.8 g/cm³). It was also determined by XRDanalysis that the film is MgS-dominated. RBS showed the stoichiometryMg:S=1:1.

Based on the results of this experiment, it was determined that suitablereaction condition would include the following: reaction temperaturefrom about room temperature (e.g., 18° C.) to about 400° C., morepreferably from about 50° C. to about 375° C. and most preferably fromabout 100° C. to about 350° C., pulse time of between about 0.025seconds to about 60 seconds, pressure ranging from about 0.5 Torr toabout atmospheric pressure (i.e., 760 Torr).

EXAMPLE 3

In this example, a comparison was made between two metal oxidesemiconductor capacitors (MOSCAPs) formed on respective InGaAssubstrates. A first MOSCAP was formed with an Al₂O₃ interface layer, anda second MOSCAP was formed with an MgS interface layer formed accordingto the present disclosure in which Mg(Cp)₂ served as the metalprecursor, and H₂S served as the sulfur precursor. The respectivefeatures and results obtained are contained in Table 1 below.

TABLE 1 Comparison of physical properties using MgS vs. Al₂O₃interfacial layers. Metric Benchmark Layer MgS Interface Layer StructurePt gated MOSCAP Pt gated MOSCAP on In_(0.53)Ga_(0.47)As onIn_(0.53)Ga_(0.47)As Ex-situ pretreatment HCl wet clean HCl wet cleanIn-situ pretreatment H₂S H₂S Interface Layer — MgS deposited with 11cycles to achieve a thickness between ~10 Å and ~15 Å High-k Layer 10 ÅAl₂O₃ and 10 Å Al₂O₃ and 30 Å of HfO₂ 30 Å of HfO₂ Post high-k H₂/N₂annealing at H₂/N₂ annealing at treatment 400° C. 400° C. CET 1.6 nm 2.3nm Dit at midgap ~1.4E12 <4E11 (eV−1cm−2) Dispersion at 1 V 4.5 0.8(%/dec)

As shown in Table 1 above, the MgS interfacial layer achieved a markedimproved over the Al₃O₂ interfacial layer particular with respect todispersion, which is a reference to the variability of capacitance atvarious frequencies. FIG. 5 illustrates the undesirable dispersionresulting from the use of an Al₃O₂ interfacial layer. FIG. 6 illustratesthe drastic reduction in dispersion obtained by using an MgS interfaciallayer formed according to the present disclosure. A lower dispersionindicates that the interface layer contains fewer defects.

EXAMPLE 4

Similar to Examples 1-3, a number of MOSCAP structures were formed, somewith interface layers of various compositions and thicknesses and somewithout interface layers, and their respective properties were measured.Each of the sample structures were formed on InGaAs channels.

In each sample, the substrate surface was first pretreated with a 1minute exposure to 37% HCl then washed twice for 15 seconds each timewith D1 H₂O followed by an exposure to H₂S at 250° C.

These various films demonstrated the benefits achieved by including aninterfacial layer comprising a metal sulfide. In particular, it wasdetermined that the use of a metal sulfide thin film as an interfaciallayer between a high-mobility channel and a dielectric layersubstantially reduced the frequency dispersion of thecapacitance-voltage curves of the films. Among the various structuresformed, a variety of dielectric materials were used, such as Al₂O₃,AlSiO_(x), HfO₂, HfSiO_(x), and TaSiO_(x). In a set of controlstructures, a thin film of aluminum oxide was used as an interfacelayer. The structures that did not include a metal sulfide interfacelayer generally exhibited a dispersion as low as 4 and as high as 8.8with an average of 5.6 and a median of 4.9. Among the structures thatincluded a metal sulfide interface layer, the dispersion was as low as0.7 and as high as 3.8 with an average of about 1.74 and median of 1.2.

Based on this example, it was determined that using a high-k dielectricdirectly on an InGaAs nigh-mobility channel did not achieve desirableresults. In contrast, a MgS interfacial did achieve desirable results.It was also determined that a pretreatment using TMA provided limited orno benefit.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. The described features, structures,characteristics and precursors can be combined in any suitable manner.Therefore, it should be clearly understood that the forms of the presentinvention are illustrative only and are not intended to limit the scopeof the present invention. All modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

We claim:
 1. A method of forming a three-dimensional structure on asurface of a semiconductor substrate in a reaction space comprising:depositing a magnesium sulfide film having a thickness of about 1 Å toabout 50 Å on the surface of the semiconductor substrate by one or moredeposition cycles comprising alternately and sequentially contacting thesemiconductor substrate surface with a first vapor-phase magnesiumreactant and a second vapor-phase reactant comprising sulfur; subjectingthe magnesium sulfide film to a post deposition treatment; and forming acapping layer having a thickness of about 5 Å to about 200 Å over themagnesium sulfide film.
 2. The method of claim 1, wherein the postdeposition treatment comprises exposure to one or more of HCl, HF, H₂S,(NH₄)₂S, H₂ plasma, and NF₃.
 3. The method of claim 1, wherein the postdeposition treatment comprises a thermal H₂ bake.
 4. The method of claim1, wherein the post deposition treatment comprises annealing at atemperature of about 300° C. to about 800° C.
 5. The method of claim 4,wherein the annealing is carried out in a forming gas atmosphere.
 6. Themethod of claim 1, additionally comprising forming a metal gate over thecapping layer.
 7. The method of claim 6, wherein the metal gatecomprises one or more of Ti, Al, Zr, Hf, V, Ta, Nb, Cr, Mo, W, Co, TiN,TiC, TiAlC, TaC, TaAlC, NbAlC, TiAl, TaAl, TaN, TaCN, WN, and TiWN. 8.The method of claim 1, additionally comprising forming a barrier layerover the capping layer.
 9. The method of claim 8, wherein the barrierlayer comprises TiN.
 10. The method of claim 1, wherein thesemiconductor substrate surface is contacted with the second reactantcomprising sulfur before being contacted with the first magnesiumreactant.
 11. The method of claim 1, wherein the magnesium sulfide filmcomprises at least one metal other than magnesium.
 12. The method ofclaim 1, wherein first magnesium reactant comprises at least onecyclopentadienyl ligand.
 13. The method of claim 12, wherein the firstmagnesium reactant is Mg(Cp)₂ or a derivative thereof.
 14. The method ofclaim 1, wherein the second reactant comprising sulfur is H₂S.
 15. Themethod of claim 1, wherein the magnesium sulfide film has aconcentration of charge trapping sites (D_(it)) of less than 5E11 1/cm².16. The method of claim 1, further comprising exposing the semiconductorsubstrate to a pretreatment reactant either ex situ or in situ prior todepositing the magnesium sulfide thin film.
 17. The method of claim 1,wherein the capping layer comprises a dielectric material.
 18. Themethod of claim 1, wherein the capping layer comprises Al₂O₃ or HfO₂.19. The method of claim 1, wherein the semiconductor substrate surfacedoes not comprise silicon.
 20. The method of claim 1, wherein thesemiconductor substrate surface comprises InGaAs.